The present invention relates to processes for printing arbitrary textile fiber materials, including all cellulosic fabrics and blends with synthetic fabrics, using inks composed of disperse dyes, in accordance with the ink jet printing process.
Conventional textile printing methods include rotary and flat-screen printing. Traditional analog printing typically involves the creation of a plate or a screen, that is, an actual physical image from which ink is transferred to the textile. However, unless the total printed yardage is sufficiently large, these conventional processes are neither economical nor practical. Conversely, because digital textile printing enables immediate printing of an electronic image, ink jet printers are now gaining rapid acceptance for sampling and small-quantity production and there is every expectation that digital textile printing will eventually supplant screen printing. Ink jet printing is a non-contact printing method in which picoliter ink droplets are deposited on some arbitrary ink-receptive substrate, according to the intended application.
Digital textile printing enables designers and manufacturers to immediately visualize a finished design. Furthermore, ink jet printing technology allows for superior textile design possibilities, in terms of the range of colors, the complexity of patterns, the ability to generate photorealistic images, and the prospect of creating non-repeating infinite patterns. The ability to quickly modify designs is quite simply enabled through textile design software, obviating a variety of costly and time-consuming steps, including screen engraving, machine set-up, and printing. Actual fabric samples of new designs are therefore generated both economically and expeditiously. Moreover, digital textile printing enables cost-effective short run production, thus accelerating the development of new products. And because printed fashion styles change quickly or are unpredictable, digital textile printing is clearly an ideal method of printing personal apparel and home furnishings, in which today's print patterns are subject to the whims of a changing market.
There are a number of problems in printing fabrics by the ink jet process that must still be addressed, however. Because the inks which are deposited onto fabric by the ink jet process are characterized by a very low viscosity, they are prone to spreading on the fabric; moreover, fabric texture may enhance or promote ink spreading. Invariably, some post-printing process, such as steaming or heat curing, which enables chemical and/or physical fixation of the dyes, is another critical aspect of textile printing, in general, and digital textile printing, in particular. Even after post-processing, dyes are often incompletely fixed within the fibers of the fabric, thus necessitating additional washing and drying steps in order to completely remove unfixed dyes from the fabric. Moreover, the printed textile images are often not detergent-resistant, resulting in fading of the printed image after washing by the consumer. Therefore, there remains a need to substantially enhance the permanence of printed textile images. It is especially desirable to eliminate the steaming post-printing process and to replace this time-consuming, inefficient process with a simple post-printing heating step, as per techniques and machinery that are common to both the analog and digital sublimation printing industries.
Because ink jet inks are prone to spreading on textile substrates, it is quite necessary to pretreat the fabric, in order to prevent the spreading of the ink. Among the inks that have been used for ink jet textile printing, sublimation inks incorporating disperse dyes have been used in one of two primary textile printing processes: 1) a direct sublimation or direct-to-textile printing method, wherein a dye-based or pigment-based disperse ink is directly printed onto a textile fabric, which is then followed by a heat treatment process, such as steaming or thermofixation, in order to permanently fix the dyes within the fibers of the fabric substrate; and 2) a sublimation heat transfer printing method, wherein, after a dye-based or pigment-based disperse ink is printed onto an intermediate sheet medium, e.g., specialized transfer paper, the sheet medium is then placed in intimate contact with a textile substrate, under a prescribed time, temperature, and pressure protocol, thus enabling the dye-based image to impregnate the textile substrate by sublimation heat transfer. The sublimation ink is in the form of a liquid obtained by emulsifying or dispersing the sublimation dye or the sublimation pigment into an aqueous or non-aqueous solution, including water, a water-soluble organic solvent, and a dispersant.
Sublimation printing is well-known in the art, having been practiced long before the emergence of digital textile printing and the use of sublimation inks in that context. Application of sublimation ink to a temporary transfer sheet may be accomplished by a number of well-known printing methods, such as rotogravure, offset lithography, or flexographic printing. The temporary support medium is then brought into intimate contact with the textile substrate, typically a 100% polyester or other synthetic fabric. The application of heat and pressure for a prescribed period of time induces sublimation of the disperse dyes from the transfer sheet, facilitating their transfer from the temporary support medium and into the fibers of the textile substrate, where they are physically impregnated and thus become a permanent part of the textile fabric.
However, it is equally well-known in the art that there has never been a single successful attempt to print cotton and other natural fiber fabrics by either direct sublimation or sublimation transfer of disperse dye inks. It may be shown, generally, that any fabric containing a cellulosic fiber, such as cotton or rayon, and printed either by direct sublimation or sublimation dye transfer will not be satisfactorily printed with the ink. For example, sublimation printing of any fabric consisting of cotton or a mixture of cotton and polyester fibers results in completely unsatisfactory printed images. Therefore, prior art methods have also included some type of fabric pretreatment or coating, or else a pretreatment of the sublimation dye transfer medium itself, with various chemicals and coating compositions, in order to enable cotton or other natural fibers to accept sublimable dyestuffs. However, all of these methods suffer from very poor performance, particularly with respect to the poor quality of the colors and/or the unacceptably low fastness of the dyes to repeated washing. Hence, while various pretreatments have been proposed over the past several decades, in order to enable cellulosic fibers or cellulosic fibers in blends with synthetic fibers, to be printed with sublimation inks, these pretreatments have invariably resulted in very poor color, unacceptable fastness, or acceptable color and/or fastness but a stiff and quite unacceptable fabric hand.
The present invention involves both direct disperse dye sublimation printing, as well as sublimation transfer, in which printing yields a dyed fabric having a very soft hand and bright, vibrant colors, and which is washfast to repeated laundering. The invention includes a novel fabric pretreatment composition and the methods for its application. The present invention is particularly innovative insofar as it allows for the first time, sublimation printing of fabrics made from natural fibers, including all cellulosics, such as cotton, in addition to fabrics composed of blends of natural and synthetic fibers. The method and compositions of this invention produce, for the first time, a sublimation fabric made of natural fiber or blends of natural and synthetic fibers, characterized by vibrant colors which will tolerate repeated laundering, without any color fading whatsoever.
It is an object of the present invention to provide pretreatment compositions for direct disperse sublimation printing or sublimation heat transfer printing of disperse dyes onto fabrics comprising substantial amounts of cotton or other natural fabrics. Accordingly, it is also an object of the present invention to provide textile printing methods which do not require steaming post-processing of arbitrarily constructed fabrics, including all cellulosic fabrics, as well as fabrics composed of blends of natural and synthetic fibers. Another object of the present invention is to provide a universal fabric pretreatment composition which makes it possible, for the very first time, textile printing of arbitrarily constructed fabrics, using only one type or class of ink, namely disperse dye ink, using any digital ink jet printing machine, capable of printing disperse dye inks, and furthermore, which is also applicable to all sublimation heat transfer processes which derive from analog (paper) printing processes. These processes include screen printing, gravure printing, and offset lithographic printing of the transfer paper substrate, using inks composed of disperse dyes.